1. Field of the Invention
The present invention relates generally to devices and methods for performing external chest compression as a part of cardiopulmonary resuscitation procedures. In particular, the present invention relates to the use of devices which provide for alternately compressing and actively expanding a patient's chest to induce both ventilation and blood circulation.
Sudden cardiac arrest is a major cause of death worldwide and can arise from a variety of circumstances, including heart disease and trauma such as electrical shock and suffocation. To improve a patient's chance of survival (and diminish the likelihood of brain and heart damage resulting from oxygen deprivation), it is essential that measures be taken as soon as possible to at least partially restore the patient's respiration and blood circulation. Approximately thirty years ago, techniques for external chest compression, generally referred to as cardiopulmonary resuscitation (CPR), were developed and have enjoyed great success in reducing mortality resulting from sudden cardiac arrest. Such techniques, however, have remained largely unchanged over the past two decades.
External chest compression relies on actively applying pressure to the patient's chest in order to increase intrathoracic pressure. Such pressure increase will induce blood movement from the region of the heart and lungs through the peripheral arteries, thus partially restoring the patient's circulation. Phase 1 of traditional CPR is referred to as the "active compression phase" where the chest is compressed by the direct application of external pressure. Phase 2, referred to as the "relaxation phase," occurs when pressure is withdrawn and the natural elasticity of the patient's chest wall causes expansion. While such expansion is generally sufficient to refill the cardiac chambers with some blood, it is insufficient to ventilate the patient, i.e., fill the lungs with sufficient air to oxygenate the blood. Thus, conventional CPR further requires periodic ventilation of the patient, e.g., mouth-to-mouth ventilation, in order to provide the air necessary for blood oxygenation.
Manual CPR procedures generally require performers to kneel over the patient and to apply pressure using the palms of their hands to the patient's sternum as the patient lies supine on a flat surface. If no one else is available, the performer must periodically shift position to ventilate the patient through a mouth-to-mouth procedure. Such manual procedures are thus very tiring to the performer and furthermore have been found to result in only limited restoration of respiration and circulation.
Manual CPR procedures can also result in injury to the patient. For example, pressure applied by the palm of the hand can fracture the patient's sternum and/or ribs and cause other traumatic injury, especially if the performer's hand position is inadvertently shifted laterally to an improper location on the patient's chest.
The performance and safety of CPR procedures can be enhanced through the use of various mechanical and automatic machines for applying external chest compression and optionally ventilating the patient by providing supplemental oxygen or air. The machines may be as simple as a "cardiac press" which is a manually operated lever which provides a mechanical advantage in performing chest compression. More sophisticated machines can provide chest compression and/or ventilation through a variety of other mechanisms, including the use of pressurized chambers for compressing the chest cavity. While such machines can be very effective, their bulk, weight, and cost limit their availability. In particular, such machines are not widely available outside of medical facilities and their size is a deterrent to providing such equipment in emergency vehicles.
CPR is often administered in conjunction with other procedures which, taken together, are referred to as advanced cardiac life support (ACLS). Most commonly, CPR is administered while the patient undergoes both electrocardiographic monitoring (ECM) and electrical defibrillation. Both ECM and defibrillation require the attachment of electrodes to the patient's chest. The need to attach electrodes can interfere with the ability to administer CPR, particularly the ability to administer manual CPR. In the case of manual CPR, the performer can also be exposed to electrical shock when current is applied to perform defibrillation.
It would therefore be desirable to provide improved devices and methods for performing external chest compression in conjunction with CPR and ACLS procedures. It would be particularly desirable if such methods and devices provided enhanced ventilation and blood circulation in the patient undergoing treatment, preferably reducing or eliminating the need to separately ventilate the patient. Desirably, the methods and devices should be simple and easily stored so that they can be maintained in emergency vehicles, non-medical facilities, and even the home. The devices should be suitable for performing enhanced manual CPR, in particular by converting Phase 2 chest expansion from a passive event to an active process to improve venous blood return from the heart and enhance airflow into the lungs (facilitated ventilation). The devices should further facilitate the simultaneous performance of electrocardiographic monitoring and/or electrical defibrillation, preferably reducing the performer's exposure to electrical shock from the electrode attachment.
2. Description of the Background Art
U.S. Pat. No. 4,881,527, describes a chamber which may be placed over a patient's chest to alternately apply pressure and vacuum to compress and expand the chest. U.S. Pat. Nos. 4,429,688 and 4,196,722, describe hand-held vacuum cups which are intended for applying percussive therapy to the lungs (chest physiotherapy). The devices are intended for repeatedly striking a patient's chest, not for applying a continuous compression and expansion. A variety of vacuum cup designs have been proposed as body massage devices. See, for example, U.S. Pat. Nos. 2,879,765; 2,742,251; 1,460,927; and 728,003, and British Patent Specification 274,306. German Patentschrift 468358 may also be pertinent.
A device for applying pressure and vacuum to a patient's abdomen to assist in breathing was described by Dr. Rudolf Eisenmenger in Wiener Medizinische Wochenschrift, page 807, Aug. 5, 1939. The device is further described in a brochure of the Biomotor Company, Munich, Germany, undated.
Anecdotal reports of the use of toilet plungers for performing CPR have been made by one of the inventors herein. See, Lurie et al. (1990), Journal of the American Medical Association, Oct. 3, 1990, page 1661; and San Francisco Examiner, article entitled "Toilet Plunger Successful in CPR," October 1990.
The use of mechanical devices for performing chest compression and CPR is described in Textbook of Advanced Cardiac Life Support, Chapter 4, American Heart Association, Second Edition, 1987.
The full disclosures of each of these references are incorporated herein by reference.